1. Field of the Invention
The invention relates to a data bus device intended for cooperation with at least one apparatus and constructed to communicate with further data bus devices which cooperate with at least one further apparatus via a data bus and comprising data-bus set-up means adapted to generate a reference table after the occurrence of a bus reset, the reference table containing data-bus device information for each further data bus device of a further apparatus connected to the data bus device, the data-bus device information identifying the further apparatus and its further data bus device until the next occurrence of a bus reset, and first memory means in which the data-bus device information contained in the reference table can be stored, and additional-information request means adapted to request additional information from a further data bus device identified by data-bus device information and to store received additional information in the first memory means in allocated relationship to the data-bus device information of the further data bus device, and communication means arranged to receive data from the apparatus which cooperates with the data bus device and adapted to supply the data to a further data bus device identified by data-bus device information, and second memory means which store manufacturer's apparatus information identifying the apparatus which cooperates with the data bus device.
The invention further relates to an apparatus including a data bus device constructed to communicate with further data bus devices which cooperate with at least one further apparatus via a data bus and comprising data-bus set-up means adapted to generate a reference table after the occurrence of a bus reset, the reference table containing data-bus device information for each further data bus device of a further apparatus connected to the data bus device, the data-bus device information identifying the further apparatus and its further data bus device until the next occurrence of a bus reset, and first memory means in which the data-bus device information contained in the reference table can be stored, and additional-information request means adapted to request additional information from a further data bus device identified by data-bus device information and to store received additional information in the first memory means in allocated relationship to the data-bus device information of the further data bus device, and communication means arranged to receive data from the apparatus including the data bus device and adapted to supply the data to a further data bus device identified by data-bus device information, and second memory means which store manufacturer's apparatus information identifying the apparatus including the data bus device.
2. Description of the Related Art
A data bus device of the type defined in the first paragraph and an apparatus of the type defined in the second paragraph are known, for example, from a commercially available and, consequently, known apparatus, namely, from a digital video camera marketed by Sony under the type number DCR-PC7. The known data bus device of the known apparatus is adapted to communicate with further known data bus devices in accordance with the data bus standards IEC1883, IEEE1394 and AV/C-CTS connected to the data bus. In the known data bus device, a bus reset is initiated when a further data bus device is connected to the data bus, or when a further data bus device is disconnected from the data bus, or when data transmission problems occur in the communication via the data bus of one of the apparatuses connected to the data bus. In order to identify data bus devices which are connected to the data bus, the data-bus set-up means of all the data bus devices connected to the data bus define data-bus device information, also known as physical ID, after every bus reset. Data-bus device information defined for a data bus device serves as address information for further data bus devices when data is transmitted to this data bus device.
After data-bus device information has been defined upon a bus reset, the additional information request means of the data bus device can request additional information from the further data bus devices connected to the data bus. Additional information can then be formed by information which specifies the nature of an apparatus which cooperates with a data bus device, i.e., whether said apparatus is, for example, a video recorder, a TV set, a set-top box or a personal computer. Moreover, additional information can be information which specifies the maximum data transmission rate of the data bus device, or a variety of further information relating to the data bus device or to an apparatus which cooperates with the data bus device. The first memory means of a first known data bus device can store additional information requested by the first data bus device and relating to a second known data bus device identified by second data-bus device information, storing being effected in a manner associated with the second data-bus device information of the known second data bus device.
However, it has been found that upon each occurrence of a bus reset in the known data bus device of the known apparatus, the additional information already stored in the first memory means can no longer be allocated to the data bus devices connected to the data bus as a result of the newly defined data-bus device information and must be requested again by the additional information request means. The new request for additional information considerably slows down the communication after a bus reset, as a result of which, the data bus must be designed for very high data transmission rates and the known data bus devices must have a high processing speed.
Moreover, it has been found that a communication between data bus devices connected to the data bus, which communication has been interrupted by a bus reset, can be delayed so long by the new request for additional information that the communication is wholly disrupted. This may result, for example, in an image dropout in the reproduction of a movie transmitted from a video recorder to a TV set via the data bus.